Reiter Syndrome: affects the sacroiliac joints and lower limbs of young men; the radiographic hallmark is a specific area of bony erosion at the Achilles tendon insertion on the posterior superior margin of the calcaneus. Involvement is usually bilateral, and arthritis, urethritis and conjunctivitis are characteristic of this syndrome. Reiter syndrome is caused by a previous infection of the gastrointestinal tract such as salmonella or by a sexually transmitted infection.